1. Field of the Invention
The present invention relates to an intake air control device for an internal combustion engine, the device comprising reed valves mounted in an intake passage to prevent a back flow of intake air and exhaust gases.
2. Description of the Related Art
An intake air control device similar to the above was filed as Japanese patent application No. 2-322671, by the present applicant. This intake air control device comprised reed valves, each mounted at side walls of a reed valve assembly body formed in the shape of a hollow square column and surrounding a control valve arranged downstream of the reed valves, instead of a single reed valve mounted at a control valve. Accordingly, when the control valve is closed, a maximum amount of intake air supplied via the reed valves is increased, whereby it is possible to supply the intake air via the reed valves not only during a low engine speed and high engine load driving condition, but also during a middle engine speed and high engine load driving condition, as in practice an engine is frequently driven in the middle engine speed and high engine load driving condition. A back flow of intake air and exhaust gases during this driving condition is also prevented by the reed valves, and thus a higher torque can be obtained to thereby increase the charging efficiency.
The back flow of intake air and exhaust gases is prevented to raise an inside pressure of an intake passage between an intake valve and the reed valves in a compression stroke, and accordingly, a capacity of the intake passage between the intake valve and the reed valves is preferably reduced, to increase the efficiency of the prevention of the back flow, and therefore the reed valve assembly is arranged at a position relatively close to the intake valve.
An inertia supercharging is generally carried out, to increase the torque in a high engine speed condition, and this requires a relatively long intake passage having a substantially uniform section between the intake valve and a surge tank as an open end.
Nevertheless, the intake passage to which the above intake air control device is mounted is provided with an enlarged portion so that the reed valve assembly can be mounted in a position relatively close to the intake valve, but this enlarged portion forms an open end, and thus the effect of an inertia supercharging cannot be obtained under a high engine speed condition.